Autism spectrum disorders, in this publication, include Autistic disorder, Asperger’s disorder, Rett's Syndrome, Childhood Disintegrative Disorder and Pervasive Developmental Disorder – not otherwise stated, which is also known as atypical autism.

The data for this publication was drawn from the 2012 Survey of Disability, Ageing and Carers (SDAC). This survey was designed to measure the prevalence of disability in Australia and the extent to which specific conditions are associated with disability. The SDAC identifies disabling conditions by first asking whether people are limited in a particular aspect of function (e.g. do they have any problems with their sight? Do they have difficulty learning or understanding things?) and then asks whatis the main condition causing that limitation. The SDAC is not a diagnostic survey and it doesn't aim to identify whether people have specific conditions based on symptoms they experience. Nor is it a health survey and is therefore not designed to provide estimates of the prevalence of specific health conditions. As a result, the data may underestimate the overall prevalence of autism spectrum disorders.

The survey has two components:- in the household component trained interviewers conduct personal interviews at private dwellings throughout Australia to obtain detailed information about aspects of peoples disabilities, the types and frequency of assistance with activities they need, and details of assistance they provide to others to enable them to participate in daily activities. The household component relies on reporting of conditions by the respondent or, if they are unable to provide the answers, someone in their family responding to the survey on their behalf. In the Establishments component a small questionnaire is sent to a sample of residential care facilities (hospitals, nursing homes, etc.) which asks about the nature of residents disabilities and the assistance they need with everyday activities. People in the establishment component of the survey (approx. 10,400 respondents) had information supplied by a member of staff of the health care establishment within which they lived.

The SDAC interviewed people living in private homes and a range of different accommodation options. It did not include people who were in gaol or were homeless. There is some evidence to suggest that people with autism may have a higher rate of homelessness, but details of the situation in Australian gaols are unknown (ENDNOTE 2). There were no changes to the SDAC questions or approach between the 2009 and 2012 versions that would have effected the identification of people with autism.